1. Field of the Invention
The present invention relates to a liquid crystal display device and a defect repairing method therefor, and more specifically, to a liquid crystal display device which allows disconnection defects caused in the process of manufacturing the liquid crystal display device to be readily repaired with a higher success rate than conventional cases, so that the device can be modified into a non-defective device, and a defect repairing method therefor.
2. Description of the Related Art
Active matrix type liquid crystal display devices used as a display device in OA-related equipment including computers have attracted attention as a high picture quality flat panel display. The liquid crystal display device has a redundant structure which can repair disconnection defects caused in the manufacturing process, in order to increase the manufacturing yield. The general structure of a conventional liquid crystal display device will be now described in conjunction with FIGS. 27 to 29.
FIG. 27 is a view of the surface of an array substrate for a liquid crystal display panel in a conventional liquid crystal display device, viewed from the liquid crystal layer side. As shown in FIG. 27, a plurality of data bus lines (drain bus lines) 11a, 11b, 11c, etc. extending in the vertical direction in the figure are formed on the substrate. A plurality of gate bus lines 13a, 13b, etc. denoted by the broken line extending in the horizontal direction in the figure are also formed on the substrate. Pixels are formed in regions defined by these data bus lines 11a, 11b, 11c and the gate bus lines 13a, 13b. In the vicinity of crossing positions of the data bus lines 11a, 11b, 11c and the like and the gate bus lines 13a, 13b and the like, TFTs 15a, 15b, etc. are formed.
For example, in the case of the TFTs 15a and 15b as shown in the upper part of the figure, drain electrodes 17a, 17b are led out from the data bus lines 11a, 11b shown at the left of the TFTs 15a, 15b, and their ends are formed to be positioned on one end side on channel protection films 19a, 19b formed on the gate bus line 13a. 
Meanwhile, source electrodes 21a, 21b are formed to be positioned on the other end side on the channel protection films 19a, 19b. In this structure, the region of the gate bus line 13a immediately under the channel protection films 19a, 19b serves as a gate electrode for these TFTs 15a, 15b. Although not shown, a gate insulating film is formed on the gate bus lines 13a, 13b, on which an active semiconductor layer forming a channel is formed. In the TFT structure as shown in FIG. 27, gate electrodes are not formed in the manner in which they are led out from the gate bus lines 13a, 13b, but a part of the linearly provided gate bus lines 13a, 13b is each used as a gate electrode.
A storage capacitor bus line 23 is formed in the region denoted by the broken line extending in the horizontal direction virtually in the center of the pixel region. Storage capacitor electrodes 25a, 25b are formed for each pixel at an over layer of the storage capacitor bus line 23 through an insulating film. Pixel electrodes 27a, 27b of a transparent electrode material are formed at an over layer of the source electrodes 21a, 21b and the storage capacitor electrodes 25a, 25b through a protection film. The pixel electrodes 27a, 27b are electrically connected with the source electrodes 21a, 21b through contact holes 29a, 29b provided in a protection film formed at the under layer. The pixel electrodes 27a, 27b are also electrically connected with the storage capacitor electrodes 25a, 25b through contact holes 31a, 31b. 
The TFT described above has an inverted staggered structure, while there are thin film transistors having other structures such as a staggered type or planar type structure having a drain electrode at the lowermost layer for example and a gate electrode at an over layer of thereof. In any of these structures, each metal layer is placed through an insulating film.
Each of the gate bus lines 13 has lead-out portions 33a, 33b, etc. led out into the pixels perpendicularly to the extending direction of the bus line. The lead-out portion 33b for example has a region overlapping the pixel electrode 27b at the upper right part of the pixel when viewed in the normal direction to the panel surface. FIG. 28 shows a section of the lead-out portion 33a taken along line E-Exe2x80x2 in FIG. 27. As shown in FIG. 28, the gate bus line 13a is formed on a glass substrate 35. The lead-out portion 33b is formed as it is led out to the side of the gate bus line 13a. A gate insulating film 37 is formed immediately on the gate bus line 13a, and the pixel electrode 27b is formed on the lead-out portion 33b through a protection film 39.
For example, as shown in FIG. 27 in the upper right part, when the gate bus line 13a is disconnected at a disconnection portion 41, the defect is repaired as follows. More specifically, the disconnection portion 41 is located between the TFT 15b and the data bus line 11c, and therefore a laser beam is irradiated upon a laser irradiation position 43 shown at the upper right corner of the pixel electrode 27b. The irradiation energy of the laser beam causes the pixel electrode 27b and the metal forming the lead-out portion 33b immediately below to be melted, connected and short-circuited. Thus, the right end of the disconnection portion 41 of the gate bus line 13a is electrically connected with the pixel electrode 27b through the lead-out portion 33b. 
Similarly, a laser beam is irradiated upon laser irradiation positions 45 on the side of the source electrode 21b of the TFT 15b to short-circuit the source electrode 21b and the left end of the disconnection portion 41 of the gate bus line 13a. A laser beam is also irradiated upon a laser irradiation position 47 shown on the proximal side of the data bus line 11b to electrically isolate the drain electrode 17b from the data bus line 11b. Thus, the disconnection portion 41 of the gate bus line 13a is short-circuited by the pixel electrode 27b and the disconnection defect is repaired.
According to the above-described defect repairing method, the repair success ratio can hardly be increased.
FIG. 29 is a sectional view of the device when a laser beam is irradiated upon the laser beam irradiation position 43 shown in FIG. 27. The distance d between the lower layer gate bus line 13a and the upper layer pixel electrode 27b is for example as thick as 800 nm. Therefore, as shown in FIG. 29, if the metal forming the lower layer gate bus line 13a as thick as 100 nm for example melts with the irradiation of a laser beam 49, only a small area is short-circuited with the upper layer pixel electrode 27b, and sometimes almost no short circuit is formed.
In order to reduce the manufacturing cost, it is strongly desirable to improve the manufacturing yield. As one means therefor, there is a strong demand to increase the repair success rate for repairing defect portions.
It is an object of the present invention to provide a liquid crystal display device which allows disconnection defects caused in the manufacturing process to be readily repaired with a higher success rate than conventional cases so that the device can be modified into a non-defective device, and a defect repairing method therefor.
The above-described object is achieved by a liquid crystal display device including a lead-out portion led out from a bus line formed on a substrate and extending at an under layer of a pixel electrode through an insulating film, and an isolated intermediate conductive layer formed in the insulating film between said lead-out portion and said pixel electrode.
According to the present invention, the thickness of the insulating film between the bus line and the pixel electrode is divided by the intermediate conductive layer. Therefore, a short-circuit interval by laser beam irradiation is reduced as compared to the conventional case and a repair success rate is improved.